1. Field of the Invention
This invention relates to the field of data storage using magnetic disk drives; for example, magnetic disk drive data storage. More specifically, the invention pertains to the field of predicting failure of a disk drive due to an increase in head to disk stiction, friction, and other physical phenomenon that affect the breakaway current and/or spin current of the disk drive""s spindle motor
2. Description of the Prior Art
The spindle or disk drive motor (i.e., the motor that rotates the spindle on which disks are mounted) of a Direct Access Storage Device (DASD) must be provided with enough current to first break the heads of the device away from physical contact with the disks, and thereafter bring the spindle motor to a stable spin condition. If the spindle motor has insufficient power to break the heads free of the disk surfaces, or if the motor has insufficient power to bring the disks up to operational rotating speed, the disk drive will not operate properly.
As used herein, the term breakaway current is the magnitude of the spindle motor energization (for example, current) that is necessary to overcome stiction, and other forces that cause the head to adhere to the surface of a stationary disk, whereas the term spin energization is the magnitude of spindle motor energization that is required to achieve a stable spin velocity of the disks and the spindle motor. In many disk drives, the magnitudes of these two electrical parameters are equal; however, they are usually not of the same magnitude in that the magnitude of the spin parameter is usually lower than the magnitude of the breakaway parameter.
Stiction is an art term that is used to define the sticking of read/write transducing heads to a recording disk surface when the disk is stationary and the heads are in physical contact with the disk. Stiction resists disk movement when the spindle motor is energized. The problem of overcoming stiction has been addressed in the art.
The publication RESEARCH DISCLOSURE, September 1991, at page 662, describes an arrangement in which, in order to assist in overcoming stiction, the disk spin motor is energized at the resonant frequency of the spin motor and its associated apparatus.
In the publication JA 60-242550, it is suggested that the head be moved radially of the disk prior to stating to rotate the disk, and in publication JA 62-295262 if energization of the disk motor does not cause movement of the disk, then a carriage motor is energized.
The publication JP 3-90840 suggests a procedure for measuring head stiction by selective rotation of a disk, and publication JP 3-105763 suggests detecting the variation in friction between a magnetic head an a recording medium, and sending a warning when the percentage of the variation factor of the friction variation exceeds a preset slice level.
Other examples contained in the U.S. patent art are as follows, which patents are incorporated herein by reference to indicate the background of the invention and to illustrate the state of the art.
U.S. Pat. No. 4,589,036 describes a disk drive unit wherein on start up the head(s) is first moved radially outward of the disk. When it is detected that the head(s) has arrived at a predetermined radial position, rotation of the disk begins. Radial movement of the head continues until disk rotation increases to a predetermined speed.
U.S. Pat. No. 4,839,754 describes the use of switching-type regulator power supply connected to a brushless DC spindle motor wherein a shunt capacitor connected to the input of the power supply operates to apply maximum possible power to the motor during start up, thus overcoming stiction-friction forces.
U.S. Pat. No. 4,970,610 overcomes the disk/head stiction effect by applying a sequence of current pulses to the disk drive motor at a frequency close to the resonant frequency of the rotary spring-mass system that is formed by the stuck assembly of disks and head suspensions.
U.S. Pat. No. 4,996,618 provides that, upon power off, the heads are moved to a disk area that is near the Contact-Start-Stop (CSS) area. Later, when power is reapplied to the disk drive unit, and before the disk rotates, a head actuator is energized to move the heads into the CSS area.
U.S. Pat. No. 5,018,029 describes the use of force perturbations to reduce the effect of stiction. Once it is detected that stiction has been overcome, operating voltage is applied to the disk""s spin motor.
U.S. Pat. No. 5,130,867 provides a piezoelectric actuator to load a head onto a disk so as to provide an operating range at a selected portion of a Stribeck diagram; i.e., a diagram that plots the friction coefficient between a head and a disk as a function of the rotational velocity of the disk.
While devices of the above type are generally useful for their intended purposes, the need remains in the art to detect or predict future disk drive failure by monitoring the electrical energization that must be applied to the spindle motor in order to cause the motor to begin to spin, and/or to cause the motor to achieve a stable spin state, wherein failure of the disk drive is predicted as a function of changes in one, or both, of these monitored electrical energizations. That is, a need remains for an insitu means for measuring and quantifying the stiction and friction present in a disk drive during use, and to use this information to alert the user to a potential failure problem before the problem actually occurs.
This invention predicts future failure of a disk drive due to a detected increase in head to disk stiction, and/or due to a detected increase in friction, and the like, that affects the ability of the drive""s spindle motor to achieve a stable spin state. An increase in stiction/friction may occur as the disk drive is used in a data processing installation, for example, as the disk drive experiences a relatively large number of stop/start cycles over a period of time. More specifically, the invention provides a method and apparatus for predicting disk drive failure by periodically measuring the breakaway current and/or the spin current of a disk drive or spindle motor. The motor""s breakaway current is the magnitude of the initial current that is required to overcome head/disk stiction and to thereby begin spinning the disk. The motor""s spin current is the magnitude of current that is thereafter required to bring the motor up to a stable and reliable spinning state whereat data processing can reliably occur. Usually, the motor""s spin current is of a lower magnitude than is its breakaway current. The invention responds to changes in breakaway current and/or spin current that may occur over a period of use, due for example, to repeated stop/start operations of the disk drive.
An object of the invention is to predict failure of a disk drive having a spindle motor, a disk that is rotated by the motor, and a head that physically engages the disk when the motor is not energized. The electrical energization that must be applied to the spin motor in order to cause head to breakaway from the disk and/or to cause the motor to begin to spin, and/or to achieve a reliable spinning state is monitored. Failure of the disk drive is predicated as a function of changes in these monitored electrical energizations.
As a feature of the invention, the rate of increase in these two motor energization parameters is compared to given magnitudes, and failure is predicted as a result of this comparison. This feature of the invention may also require that the number of disk drive stop/start operations exceed a given magnitude before the rates of increase of these two parameters are monitored.
These and other objects and advantages of the invention will be apparent to those of skill in the art upon reference to the following detailed description, which description makes reference to the drawing.